The present invention relates generally to cameras and, more particularly, to digital cameras having fixed focus and automatic focus mode features.
In general, hand held cameras may be one of two types: Automatic focus (auto-focus) and fixed focus. Before discussing the merits and characteristics of the two camera types, it will be worthwhile to consider the concepts of xe2x80x9cfocal pointxe2x80x9d and xe2x80x9cdepth of fieldxe2x80x9d for helping to gain a more clear understanding of camera operations. Focal point is generally defined as the point on the axis of the camera lens at which incident, parallel light rays converge or appear to converge. Pictures taken at the focal point of the lens will be in sharp focus and, absent any unfavorable circumstances, a clear photograph will result.
Depth of field may be defined as the distance in space over which a camera lens focused on a given object can provide adequate definition or clarity. Thus, the depth of field is the area (relative to the lens) in front of and behind the true focal point.
In this regard, the position of the lens can be adjusted, or focused, on either side of the focal point and still a sharp, clearly focused image can be produced, provided the object is within the depth of field of the lens.
Considering now the merits of fixed focus and auto-focus cameras, it is well known to those skilled in the art that a fixed focus camera is less expensive to manufacture than the auto-focus type. In this regard, the fixed-focus camera generally is incapable of affecting lens or aperture changes and relies, instead, on a large depth of field wherein the object to be photographed is perceived to be in focus. Under many circumstances this technique permits suitable picture taking of objects which are several feet away from the lens to those objects at xe2x80x9cinfinityxe2x80x9d.
However, in cases where the photographer desires to take a picture of a subject that is close to the camera, for portraits of individuals, or detailed scientific study as examples, the camera auto-focus mode is the one of choice.
While superior in some cases, auto-focus cameras are more expensive to manufacture than fixed focus cameras and, in the case of most digital cameras, they are slower in operation than the fixed focus type.
In the operation of a conventional auto-focus camera, the photographer presses the camera""s exposure button half way and holds it at this position to expose a charge coupled device (CCD). The CCD receives the incident light and converts it to a digital file of image data in the form of an analog signal. This signal is converted in turn by an analog to digital converter to a digital signal which then activates a processor controlled motor to move the lens, all the while following the steps of a control algorithm for focusing the lens. In this regard, the motor moves the lens incrementally and repetitively, until the incident light impinging the CCD produces the highest frequency data. At this point the lens is focused. Typically, the control algorithm permits an overstep of the optimum focal point and then backsteps the lens to that focal point. When this is attained, an LED (light emitting diode) display indicates to the photographer that the camera is ready to take the picture. The photographer then depresses the camera button the full distance and the picture is taken.
Performance of the above described auto-focus operation takes between 1 and 3 seconds. During this time, the photographer must wait for the camera to adjust its focal point before the picture can be taken. Since having to wait is often undesirable, it would be advantageous to have a digital camera having the auto focus-capability yet would be capable of taking pictures at a distance, without an auto-focus time delay.
The digital camera of the present invention includes a camera which powers up in a default fixed-focus mode and has a capability whereby the photographer can select an auto-focus mode. The camera includes an adjustable aperture, a lens/shutter arrangement and a motor for acting on the lens/shutter arrangement. A CCD, electrically interconnected to an analog to digital signal converter, receives frequency data and transforms the data to analogs for transmission to the converter where a digital output signal is generated. The digital signal is electrically transmitted to a processor which is electrically coupled to the motor. In the fixed focus default mode, a first control algorithm facilitates a process wherein the processor generates an electrical signal to cause the motor to move the lens directly to a control position. To elect the auto-focus mode of camera operation, the photographer depresses a button and thereby selects a process which functions in accordance with the steps of a second control algorithm. In this case, the processor generates an electrical signal to cause the motor to move the lens incrementally past a focal point, and a second signal to cause the lens to backstep to the focal point. When the auto mode is selected, an icon appears on a data liquid crystal display (LCD) to indicate that auto focus mode is selected.
The combination of the present invention provides in a novel manner the speed of a fixed-focus camera, for objects at a distance, with the capability of an auto-focus operating mode for objects that are close.